Columbium-tantalum-aluminum alloy



1,922,714 t v COLUMBIUM-TANTALUM-ALUMINUMALLOY' John L. Benham,Lewiston, N.Y., assignor to Union Carbide Corporation, a corporation ofNew York No Drawing. Application April 3, 1957 Serial No. 650,291

4 Claims. (Cl. 75-138) This invention relates to acolumbium-tantalum-aluminum alloy particularly adapted as an additivefor titanium base alloys.

Titanium exists in either of two crystallinefforms. At low temperatures,it exists in the hexagonal crystal form known as the alpha phase, and.transforms at about 885 C. into the cubic crystal form known as the betaphase. Beta alloys are generally characterized by excellent weldabilityand are admirably suited in the production of titanium sheet alloy wherebending'properties are the criterion. However, some generaldisadvantages of the beta titanium base alloys are their poor tensileductility, poor retention of strength-at elevated temperatures, and poormetallurgical stability. On the other hand, alpha titanium base alloysare much more stable and possess good retention of strength at elevatedtemperatures and good tensile ductility. The chief disadvantage of thealpha type titanium alloy is its-poor bend ductility. Because oftheincreasing use-of titanium in industry, there is a demand for a titaniumproduct having the beneficial properties of both the alpha and thebetatitanium alloys.

Certain alloying additions to a titanium base metal, among which arecolumbium and tantalum, serve to increase the structural strength oftitanium alloys. These constituents are usually added as. pure metals oras ferro-alloys, such as ferrocolumbium or ferrotantalumcolumbium. Theaddition of these, desirable constituents as relatively pure metals isan expensive procedure and has the added disadvantage of poor rate ofsolution because of the high melting points of the pure metal additives.Both tantalum ,and columbium metals are highly malleable materials and,therefore, lack the requisite brittleness to be reduced to powder form.Tantalum and columbium additions 'as commercial alloys present a problemin controlling the introduction of such deleterious elements to titaniumas oxygen, hydrogen, nitrogen, iron, carbon and silicon, which arenormally present in ferrocolumbium and ferrotantalum-columbium insubstantial percentages.

It is therefore an important object of the present invention to providean addition agent for a titanium melt that is effective in producing astable titanium base alloy having a desirable combination of goodweldability, good tensile and bend ductility, the retention of strengthat elevated temperatures, and a higher service temperature than presentday all-alpha titanium base alloys.

Another object of the present invention is to provide an addition alloyof columbium-tantalum-aluminum which can be economically used as anaddition agent for the production of a stable titanium base alloy.

Another object of the present invention is to provide an addition alloyof columbium-tantalum-aluminum' essentially free of such deleteriouselements to titanium as oxygen, nitrogen, hydrogen, iron, carbon andsilicon.

Another object of the invention is to provide an addited States Patenttion alloy of ,columbium-tantalum-aluminum which can be readily reducedtofinely divided form by means of conventional crusher apparatus.

' ,The invention by meansof which these objects are 5 achieved is, basedon .the discovery that. the addition to a titanium melt of a properly.proportioned master alloy, in which both alpha and beta phase promotersare present, produces an excellent grade of titanium alloy having anadvantageous combination of desirable characteiistics'found in all-alphatitanium alloys and all-beta titanium alloys. The master alloy of theinvention comprises as essential constituents, columbium and tantalum,which are known to retard the formation of alpha-phase titanium and tostabilizethe beta phase titanium, and aluminum which has a strongtendency to promote the formation of alpha-phase titanium. Small amountsof other elements such as iron, silicon and manganese may be present inlimited amounts, and gaseous impurities such as oxygen, hydrogen andnitrogen may bev present as incidental impurities. The addition of thesubject alloy results in a titanium alloy having a stable structurecomprising an alpha matrix in which some beta phase is present. I

In a preferred embodiment of the alloy addition of the invention, therangeof composition should be within the following limits. g 1

Preferred, percent Broad,

percent up to 2.5 up to 1.0 up to 5.5 up to 0.25 remainder Optimumresults are obtained within the above range when the ratio of columbiumto tantalum is approximately 2 to 1, the ratio of aluminum to thecombined tantalum and columbium content is 5 to 3, the iron does notexceed 4% of the combined tantalum and columbium content, the'silicondoes not exceed 1.5% of the tantalum and columbium, and the totaloxygen, hydrogen and nitrogen not exceeding 0.5% of thetantalum andcolumbium.

In Table I are set forth results obtained on analysis 5 of a typicaladdition alloy of the invention. The typical alloy addition was made ina heat in which fused columbo tantalite and crude columbium oxide of thefollowing compositions were reduced with excess aluminum in the presenceof lime to produce a tantalum-columbium alloy containing Al.

Fused Columblum Columbo- Oxide tantalite TABLE I Chemical analysisElement: Percent Ta 12.82 Al 49.85

Ti 1.79 Fe 1.45 Si 0.54 Mn 4.75

O 0.010 H 0.013 Impurities Remainder As afeature of the invention, thesubject alloy possesesjgood crushability, an important attribute whichis economically desirable in alloy additions, particularly thosecontaining tantalum and columbium constituents.

Shown in Table II below are the results of a typical screen analysis ofthe alloy specified in Table I. The alloy was readily crushed inconventional crusher apparatus.

TABLE 11 Screen analysis Retained on: Percent /4 Nil 8 Mesh 88.88

mesh 8.03

48 mesh 1.41

100 mesh 0.94 Thru 100' mesh Balance Typical mechanical properties ofdnneale d Ti base alloy sheet (.04 thick) .040 inch sheet Ultimatetensile strengthipsi.) 127, 000

Yield Strength, 0.2% offset (psi 120, 000

Elongation (percent) 16 Min. bend radius w) 34 tlnckness Welding testson the above final titanium base alloy indicated that the alloy isreadily welded with the same techniques used for commercially puretitanium, and that the weld sections possess substantially the same bendductility and mechanical properties as the unwelded sections of thealloy.

From the above it will be seen that the tantalumcolumbium-aluminummaster alloy of the present in vention isideallysuited as an additionagent to a titanium base alloy. When added to a titanium alloy, it iseffective in producing a titanium base alloy having a highly desirablecombination of properties previously occurring in part in alpha titanium"alloys and beta titanium alloys. In addition, the alloyof the inventionis easily reduced to powder form, and its use in readily preparedaccurate quantities substantially reduces production costs.

It will be understood that modifications and variations'may beetfected'without departing from the spirit and scope-of the novelconcepts of the present invention.

Whatisclaimedisz l. A columbiumtantalum-aluminumalloy consistingessentially of about 10% to 35% tantalum, 10% to 35% columbium, and theremainder aluminum and incidental impurities.

2. A columbium-t-atalum-aluminum alloy consisting essentiallyof about10% to 20% tantalum, 25% to.35% columbium, and the remainder aluminumand incidental impurities. 7

3. A columbium-tantalum-aluminum alloy consisting essentially of about10% to 35% tantalum, 10% to 35% columbium, 20% to 75% aluminum, up to 3%iron, up to 1.5% silicon, up to 7% manganese, up to 0.5% of oxygen,hydrogen and nitrogen, and the remainder incidental impurities. 1

4. A columbium-tantalum-aluminum alloy consisting essentially of about10% to20% tantalum, 25% to 35% columbium, 35% to aluminum, up to 2.5%iron, up to 1.0% silicon, up to 5.5% manganese, up to 0.25% oxygen,hydrogen and nitrogen, and the remainder incidental impurities.

References Cited in the file of this patent UNITED STATES PATENTS2,369,354 Kenipf et al. Feb. 13, 1945 2,579,369 Dawe Dec. 18, 19512,711,9 0 Methe June 28, 1955 2,740,711 Herres et Apr. 3, 1956 2,754,204Iaifee et al. July 10, 1956 2,769,707 Vordahl Nov. 6, 1956

1. A COLUMBIUM-TANTALUM-ALUMINUM ALLOY CONSISTING ESSENTIALLY OF ABOUT10% TO 35% TANTALUM, 10% TO 35% COLUMBIUM, AND THE REMAINDER ALUMINUMAND INCIDENTAL IMPURITIES.